The present invention relates generally to medical devices and, in particular, aortic cannulas. Aortic cannulas are used to return blood to the aorta while the heart is by-passed during heart surgery. These cannulas are purposely made with small diameters to minimize the disruption to the aorta, which in many heart surgery patients have advanced complex atherosclerotic plaque with adherent blood thrombi.
Aortic cannulas generally comprise an elongated tube having a terminal end. In at least some styles of conventional cannulas, a single opening is provided in the terminal end which provides a single stream of blood exiting the cannula and entering the aortic arch. Due to the small diameter of the cannula, the flow velocity of the blood through the single opening in the terminal end of the cannula is extremely high, resulting in "jet" flow. The fluid pressure at the discharge end of the prior art cannula is also high. It is believed that the force of this jet stream of blood dislodges atherosclerotic plaque and/or adherent thrombi from the walls of the aorta, causing embolisms and strokes.
Attempts in the art to prevent embolisms resulting from cannulation have included designing the cannula in order to reduce the velocity of blood exiting the terminal end. For instance, U.S. Pat. No. 5,354,288 describes a cannula having a conical diffuser placed toward the proximal end of the cannula. The cannula includes several outlet openings in the sidewall to permit blood deflected by the diffuser to flow out of the cannula. This cannula design, however, still directs blood toward the sides of the aortic arch wherein the atherosclerotic plaque usually lies. Thus, the patient is still susceptible to embolisms and strokes.
Therefore, a primary objective of the present invention is the provision of an improved aortic cannula which does not cause injury to the aortic tissues or dislodge atherosclerotic plaque during cannulation.
Another objective of the present invention is the provision of an improved aortic cannula which directs blood flow from the cannula toward the ascending aorta.
A further objective of the present invention is the provision of an improved aortic cannula which reduces the risk of embolisms or stroke present with the use of conventional cannulas.
Still a further objective of the present invention is the provision of an improved aortic cannula which decreases the jet effect of blood flow from the cannula.
Another objective of the present invention is the provision of an improved cannula which directs the blood flow approximately 90.degree. from the cannula axis and which broadcasts the blood flow through the cannula opening across a radius of approximately 90.degree..
Yet another objective of the present invention is the provision of an improved aortic cannula which is economical to manufacture and convenient, durable, and safe to use.
These and other objectives will be apparent from the following description of the invention.